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<title>SSL_do_handshake</title>
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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
  <li><a href="#NOTES">NOTES</a></li>
  <li><a href="#RETURN-VALUES">RETURN VALUES</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>SSL_do_handshake - perform a TLS/SSL handshake</p>

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code>#include &lt;openssl/ssl.h&gt;

int SSL_do_handshake(SSL *ssl);</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>SSL_do_handshake() will wait for a SSL/TLS handshake to take place. If the connection is in client mode, the handshake will be started. The handshake routines may have to be explicitly set in advance using either <a href="../man3/SSL_set_connect_state.html">SSL_set_connect_state(3)</a> or <a href="../man3/SSL_set_accept_state.html">SSL_set_accept_state(3)</a>.</p>

<h1 id="NOTES">NOTES</h1>

<p>The behaviour of SSL_do_handshake() depends on the underlying BIO.</p>

<p>If the underlying BIO is <b>blocking</b>, SSL_do_handshake() will only return once the handshake has been finished or an error occurred.</p>

<p>If the underlying BIO is <b>nonblocking</b>, SSL_do_handshake() will also return when the underlying BIO could not satisfy the needs of SSL_do_handshake() to continue the handshake. In this case a call to SSL_get_error() with the return value of SSL_do_handshake() will yield <b>SSL_ERROR_WANT_READ</b> or <b>SSL_ERROR_WANT_WRITE</b>. The calling process then must repeat the call after taking appropriate action to satisfy the needs of SSL_do_handshake(). The action depends on the underlying BIO. When using a nonblocking socket, nothing is to be done, but select() can be used to check for the required condition. When using a buffering BIO, like a BIO pair, data must be written into or retrieved out of the BIO before being able to continue.</p>

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

<p>The following return values can occur:</p>

<dl>

<dt id="pod0">0</dt>
<dd>

<p>The TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL_get_error() with the return value <b>ret</b> to find out the reason.</p>

</dd>
<dt id="pod1">1</dt>
<dd>

<p>The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been established.</p>

</dd>
<dt id="pod01">&lt;0</dt>
<dd>

<p>The TLS/SSL handshake was not successful because a fatal error occurred either at the protocol level or a connection failure occurred. The shutdown was not clean. It can also occur if action is needed to continue the operation for nonblocking BIOs. Call SSL_get_error() with the return value <b>ret</b> to find out the reason.</p>

</dd>
</dl>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/SSL_get_error.html">SSL_get_error(3)</a>, <a href="../man3/SSL_connect.html">SSL_connect(3)</a>, <a href="../man3/SSL_accept.html">SSL_accept(3)</a>, <a href="../man7/ssl.html">ssl(7)</a>, <a href="../man7/bio.html">bio(7)</a>, <a href="../man3/SSL_set_connect_state.html">SSL_set_connect_state(3)</a></p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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